Wood Shake Roof for Rainwater Harvesting
Wood Shake roofing captures 75% of rainfall that hits its surface, making it the least efficient material for rainwater harvesting. A 1,500-square-foot wood shake roof in Texas (29 inches annual rainfall) collects approximately 20,887 gal per year. Wood Shake is not recommended for potable water collection due to potential chemical leaching. It is well-suited for non-potable uses including garden irrigation, lawn watering, toilet flushing, and general outdoor use.
About Wood Shake Roofing for Rainwater Collection
Wood shake roofing, made from split cedar, redwood, or pine, provides the lowest collection efficiency of common roofing materials at 75%. The highly textured, porous surface absorbs a significant portion of each rainfall event. Cedar shakes can absorb up to 20% of their weight in water before runoff begins, meaning light rain events may produce minimal or zero collection. Once saturated, wood shake sheds water more effectively, bringing efficiency closer to 80% during sustained heavy rainfall.
Wood shake is not recommended for potable water collection. The organic wood material harbors bacteria, mold, and mildew, particularly in humid climates. Many wood shakes are treated with chemical preservatives (copper naphthenate, zinc naphthenate, or chromated copper arsenate) or fire retardants that leach into collected water. Even untreated wood releases tannins and organic acids that discolor water and can promote bacterial growth in storage tanks.
For non-potable uses, wood shake roofs can still serve as collection surfaces. Garden irrigation is the most natural match, as plants are not affected by the mild tannin content, and any microorganisms in the water are beneficial for soil biology. Use a robust first-flush diverter to discard the most contaminated initial runoff, and consider a larger-than-normal first-flush volume (2 gallons per 100 square feet rather than the standard 1 gallon) to account for the organic material that accumulates on wood surfaces. Clean your gutters more frequently than you would with other roofing materials, as wood shake generates more organic debris.
Harvest Potential by State with Wood Shake
The table below shows the annual rainwater harvest from a 1,500-square-foot wood shake roof (75% efficiency) across six representative states. Annual rainfall varies dramatically across the country, and this variation directly affects your collection potential.
| State | Annual Rainfall | Annual Harvest | Annual Savings |
|---|---|---|---|
| California | 22.2" | 12,895 gal | $96.30 |
| Texas | 28.9" | 20,887 gal | $53.50 |
| Florida | 54.5" | 37,146 gal | $53.50 |
| New York | 46.2" | 31,540 gal | $96.30 |
| Arizona | 13.6" | 7,850 gal | $47.10 |
| Washington | 38.4" | 25,792 gal | $64.20 |
Maintenance Tips for Wood Shake Collection Roofs
Wood shake roofs demand the most maintenance for rainwater harvesting. Inspect and clean gutters at least quarterly, as shake roofs generate the most organic debris of any material. Remove moss, mildew, and biological growth annually — allow this to accumulate and your water quality will deteriorate significantly. In humid climates, consider zinc or copper ridge strips that naturally inhibit moss growth through metallic runoff during rain. Replace deteriorated shakes promptly, as rotting wood introduces bacteria and contaminants. Clean the roof surface with a stiff brush (never pressure wash, which can damage the wood grain) annually before the rainy season begins.
Compare Other Roof Materials
- Metal Roofing — 95% efficiency, potable safe
- Slate — 90% efficiency, potable safe
- Clay Tile — 85% efficiency, potable safe
- Concrete Tile — 85% efficiency, potable safe
- Asphalt Shingle — 80% efficiency, non-potable only
Not sure which material is best for your needs? Use our calculator to compare harvest estimates for different roof materials with your specific roof area and location.